Frozen foods and the like are commonly packaged in cartons, trays and other container for the product, closed by a lid sealed thereto. The trays and lids are typically made of paperboard, plastic or metal foil, or of laminates comprised of combinations of such materials, and heat sealable coatings, normally of a synthetic thermoplastic resinous material, may be applied thereto if the components are not inherently sealable. Generally, the trays will have a peripheral flange portion extending laterally outwardly about their openings, against which the covering lid is secured.
The lids are generally applied and sealed automatically on high speed machines, which must therefore be capable of receiving, closing and discharging the containers, rapidly, reliably and without damage to the package. The presence of lateral flange portions on the tray introduces difficulties of machine design, not only from the standpoint of conveyance through the machine but also with regard to the ability to achieve a good seal completely about the package.
It is conventional to use a microwave technique for activation of the sealable material, and chambers are normally provided for that purpose along opposite sides of a travel path for the lidded container. This means, however, that a rectangular package must be rotated 90.degree. in order to seal all four edges, and it virtually precludes operation with containers that are not rectangular or that have flanges with curved sections.
As evidenced by the patents listed below, it is common to employ laterally disposed timing screws in packaging machinery for gating purposes. Flange portions of trays are not, however, suitable as the means by which they are engaged for movement through a machine, and consequently lateral flanges interfere with such operation involving a timing screw that is disposed alongside the travel path; moreover, such an arrangement is problematic when the containers are other than rectangular. The following U.S. patents typify the prior art in the field:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 1,667,991 Russell 2,010,196 Moller 2,011,829 Schnur 2,645,399 Bozek et al 3,200,562 Zebarth et al 3,338,027 Amberg et al 3,418,785 Duryee 3,436,894 Sorensen 3,471,992 Amberg et al 3,572,004 Carmichael 3,577,866 Ehrenfried 3,710,937 Cook 3,938,305 Jansen et al 4,002,005 Mueller et al ______________________________________
Thus, the art does not provide a lid-sealing machine or method that is optimally suited for handling trays and other containers of various configurations, having laterally outwardly extending peripheral flange portions, and it is a primary object of the present invention to satisfy such a need.
It is a more specific object of the invention to provide a novel lid-sealing machine and method for securing lids to flange portions of containers that are non-rectangular or that have curved sections thereon, wherein the seal produced extends along the entire flange and has a high level of integrity.
Another object is to provide such a machine and method wherein the system for gating the containers is adapted to convey them reliably and efficiently, regardless of their shape and of the presence of a peripheral flange portion thereon.
A further object of the invention is to provide a high-speed machine that operates continuously, reliably, effectively and efficiently to achieve optimal output rates of lid-sealed containers.